Process for the production of metallic magnesium



Patented Feb. 21, 1939 v PATENT OFFICE PROCESS FOR THE PRODUCTION OF METALLIC MAGNESIUM- Daniel Gardner, Rueil-Malmaison, France, as-

signor to Studien-& Verwertungs-Aktiengesell: schaft, Neuhausen, Switzerland, a joint-stock company of Switzerland No Drawing. Application July 29, 1936, Serial No. 93,177. In Great Britain December 23,

10 Claims.

This invention relates to processes for the production of magnesium, being concerned with the industrial production of this metal, reference to which is intended to include alloys thereof.

Heretofore magnesium has been mainlyobtained by the electrolysis of magnesium chlorideproduced from magnesium ores. A number of electrolytic processes for the production of magnesium in this manner have been proposed,but one of the main difliculties that is experienced in all electrolytic processes is that of removing from the magnesium the last traces of chlorides which remain occluded in the metal.

The present invention has for its object to produce, by a non-electrolytic process, magnesi m cheaply and of a high degree of purity from any magnesium ores or compounds of commercial value.

Already in 1867 Parkinson (Journal of the Chemical Society, Vol. V, p. 127) described the direct production of magnesium sulphide by heating magnesium filings with sulphur or sulphur vapours; hereby a hard brittle difiicultly fusible mass of impure magnesium sulphide is obtained. When obtained by indirect methods from magnesium compounds, magnesium sulphide is an unstable body which readily undergoes decomposition on exposure to air and still more moisture, whereby magnesium hydroxide is formed. Further, the formation of magnesium,

sulphide, which is of an endothermic character by prior methods takes place rather slowly.

It is to be stated, that Geelmuyden (Comptes Rendus vol. 130 of 1900, page 1029) when working on the reduction of certain sulphides by calcium carbide, has found that a mixture of magnesium sulphide (prepared by the action of hydrogen sulphide on anhydrous magnesium sulphate) and calcium carbide was heated for five mir' e a carbon tube with a current of 850 an at 45 volts, luminous flames were observed during the heating process proving volatilization of magnesium.

Magnesium sulphide as previously obtained by the direct action of sulphur on magnesium or by various indirect methods heretofore employed has nothitheito found any industrial application,

as a starting product for the manufacture of magnesium, but if special precautions be observed, in its manufacture, magnesium sulphide is easily obtainable and, under appropriate con ditions as will be hereinafter described, is a very suitable product for the manufacture of magnesium.

According to the present invention a process for the production of magnesium from magnesium ores or compounds consists in first producing magnesium sulphide by heating a magnesium compound, such as magnesia, with a carbonaceous reducing agent in sulphur vapours and/or a gaseous or vaporized non-metallic sulphur compound, such as carbon bisulphide or sulphuretted hydrogen, or without a carbonaceous reducing agent in vapours of carbon bisulphide, to a temperature sufficiently high, say within the range of about 800-1200 C; or over, to convert the bulk of the magnesium compound treated into magnesium sulphide, this reaction being carried out in an atmosphere substantially free from moisture, oxygen and air, and then subjecting the magnesium sulphide so formed to reduction by heating it with a carbide of an alkali earth metal, preferably calcium carbide, in an atmosphere of a reducing and/or inert gas and in the substantial absence of moisture, nitrogen and oxygen or oxygen-containing gases.

The reduction of the magnesium sulphide by calcium carbide takes place according to follow- 7 In order to obtain a good yield of magnesium, it is essential to use the magnesium sulphide and the carbide in a fine state of'subdivision and the reaction is effected in a gaseous atmosphere at normal or at reduced pressure.

Since magnesium sulphide readily undergoes decomposition on exposure to air and moisture, it is desirable to use it immediately for the reduction to metal, but if it is not so used the magnesium sulphide should be stored free from moisture in hermetically sealed receptacles.

A good yield of magnesium and a quick reaction are obtained by introducing into the mixture of finelyground magnesium sulphide and carbide a suitableflux, such as a chloride or a fluoride, the boiling point of which is above that at which magnesium distills. As fluxes suitable for their purpose there may be mentioned for instance anhydrous calcium chloride or a mixture of anhydrous calcium chloride and aluminium fluoride.

If no flux is added to the mixture it is advisable to come up in temperature for the reduction, say up to 1500-1600 C.

The mixture of magnesium sulphide and carthe heated zone must be preferably so chosen that the magnesium produced can be easily removed from the mixture by distillation. Astlie magnesium distills under normal pressure at about 1120" 0., it is suitable to choose a temperature above this point, say 1200 or 1250 C. It is .of course possible to choose a higher temperature if required; when working under reduced pressure the temperature can be somewhat lower.

The magnesium vapours coming from the reduction chamber are entered into special condensing chambers where they can be directly cooled and obtained in the molten or solid state. In carrying out the process, the magnesium is collected at normal pressure, in an atmosphere of hydrogen and/or an inert gas, such as argon or helium, or another gas which has no action on magnesium, for example a gaseous hydrocarbon such as methane.

If desired the collected magnesium can be directly combined with other metals such as for example aluminium or beryllium to form magnesium alloys.

The reduction of the magnesium sulphide to metal is an exothermic reaction which takes 'place rather more energetically as compared with the known reduction of magnesium oxide by calcium carbide, as mentioned in the French patent of Matignon No. 488,735.

The reduction as suggested in the present invention can be so regulated that a continuous action takes place; for this purpose, when the process is carried out under normal pressure, it is suitable to maintain in the reaction zone of the reduction furnace a temperature of 1200"- 1300 C., for instance 1250 C. As stated above magnesium thus obtained distllls under normal pressure at about 1120 C., and can be continuously collected in a condensing chamber or, if desired, it may be directly introduced into a bath of molten metal in the condensing chamber in order to produce an alloy of magnesium.

If the reaction is carried out in the absence of a flux, it may be advisable to considerably raise the temperature over 1300 0. Interesting results are obtained for instance at a temperature of about 1600 C. without a fiux; it is however,

preferable to work at about 1250 a. flux.

In carrying out the present process for the reduction of the magnesium sulphide and the distillation of magnesium, care must be taken to obtain the residual slag in the form of a dry mass which can be continuously removed from the furnace in which the reaction is effected, for instance by means of a worm conveyor. It is more dlfllcult to remove a tacky slag; therefore the formation of a tacky slag must be avoided as its removal would create difllculties.

It is desirable to provide a filter or a screen for the magnesium vapours; such filters can suitably take the form of a graphite screen, which is located at the end of the furnace chamber (reduction chamber) just in front of the outlet conduit therefrom, through which the magnesium vapours pass into the condensing chamber.

The production of the magnesium sulphide which is used in the present process for obtaining the metal can be effected by heating a magnesium compound, with or without a carbonaceous reducing agent, with sulphur vapours and/or a gaseous or vaporised non-metallic and nonoxygen-containing sulphur compound to a temperature sufficiently high, for example about 800 C. whilst using to l200 0., to convert the magnesium compound treated into magnesium sulphide, the reaction for the formation of the magnesium sulphide being carried out in an atmosphere free from moisture, oxygen and air.

In making the magnesium sulphide the necessary conditions can be realised by effecting the formation of the magnesium sulphide in the presence of sulphur vapours, sulphuretted hydrogen or derivatives thereof, carbon bisulphide in a reducing atmosphere such as hydrogen or hydrocarbons, or an inert gas such as argon or helium, care being taken that all the reagents and the atmosphere in which the reaction is effected are freed from moisture and air.

Where the atmosphere in which the reaction is carried out comprises hydrogen, it is to be observed that the hydrogen functions only as a reducing atmosphere, since hydrogen has no action either in the formation of the magnesium sulphide (for example from magnesium sulphate) or on the sulphide once the latter has been formed.

The formation of the sulphide takes place at a temperature of about 800 C. when carbon bisulphide is used. By producing the magnesium sulphide starting from magnesite calcined at low temperature (for instance 600800 C.), sulphur and charcoal (or shale, turf or lignite) the reaction temperature is suitably raised up to about 950 C. If ordinary coke were used as carbon containing material, it would be necessary to work at a higher temperature, say at about 1200 C.

Once the anhydrous magnesium sulphide has been formed, it is then reduced to metal, this being effected according to the present invention by a carbide, preferably calcium carbide, in the manner already described morein detail.

It is to be observed that the first reaction in the present process, that is to say the formation of the magnesium sulphide, is an endothermic one and requires a. somewhat lengthy time for its completion, whereas the second reaction in the process namely the reduction of the magnesium sulphide to metal, is an exothermic reaction which takes place rather energetically as compared with the known reduction of magnesium oxide by calcium carbide.

The production of the magnesium sulphide may becarried out in any suitable furnace, such as a tubular furnace provided with a suitable refractory lining. The lining may be 'made from fused magnesia, graphite or other materials resistant to vapours of sulphurgor sulphur compounds at the hereinbefore mentioned ,high temperatures. The outlet end of the furnace in which the reaction for the production of the magnesium sulphide is effected, is suitably connected with a condensing chamber, the end of said chamber being for instance closed by a suitable stopper made of refractory material. For continuous working the magnesium sulphide should be continuously removed from the furnace.

After the magnesium sulphide has been formed there is mixed with it in the furnace chamber the requisite quantity of powdered calcium carbide and powdered flux, whereby, at the high temperature prevailing, decomposition of the sulphide with liberation of the metal is efiected.

The present process is applicable to various magnesium ores and compounds, but it will of course be understood that the precise method employed for the formation of the magnesium sulphide will vary according to the nature of the u particular magnesium ore or compound treated.

Magnesium sulphide hitherto obtainedby direct action of sulphur and magnesium (Parkinson) or by various indirect methods has not found any industrial application as yet as a starting product for the manufacture of magnesium.

It may also be mentioned that products, such as sulphur or carbon bisulphide, employed in the present process in the formation of the magnesium sulphide can be recovered for reuse in the process.

The following are some examples for the manuiacture of magnesium by the new process according to the present invention.

EXAMPLE 1 Production of magnesium from magnesia in the form of coke or charcoal, the mixture introduced into the furnace and subjected at the requisite temperature to the action of sulphur vapours or sulphuretted hydrogen. The furnace in which the formation of the magnesium sulphide is effected may be heated electrically or in any other manner. Preferably the reaction mass is well mixed during the sulphidisation process in order to speed up the reaction and for this purpose the furnace employed may for instance be one of the rotary tube furnace type. The interior of the furnace must be kept free from moisture or air during the operation. After the sulphide has been formed it'is then well mixed with the requisite amount of finely powdered calcium carbide and any desired flux, the admixture taking place in the reduction furnace itself. Thereupon at the high temperature prevailing suitably But this recovery can also be carried out by the action of carbon dioxide as follows:

The present process has the advantage that the magnesium can be obtained at a temperature of between 1200-l250 C., but this temperature can be lowered if desired by carrying out the reactions under a reduced pressure.

Since the' formation of the magnesium sulphide requires a considerably longer time than the reduction to metal, these facts must be borne in mind and taken-account of in arranging the details of the process so as to operate it as a continuous one.

When the magnesium sulphide is produced from magnesia mixed with charcoal by the action of sulphur vapours, the reaction is effected by heating the mixture at about 950 C. This reaction may be expressed by the following equation:

If desired the magnesium oxide may be first of all treated with magnesium chloride, MgClz- 6H2O, the product dried and thereafter mixed with coke and treated with sulphur vapours at the temperanesium sulphide or mixture of magnesium sulphide and magnesium chloride inthe manner hereinbefore explained.

EXAMPLE 2 1 Production of magnesium from dolomite The first stage is the formation of magnesium sulphide. This is best effected by heating the dolomite at about 600,-800 C., in a furnace in order to liberate the major part of the carbon dioxide from the double carbonate. There is thus obtained a-mixture of calcium and magnesium oxides. The calcination of the dolomite can be effected either by directly heating it or by mixing with it carbonaceous materials such as coke and heating the mixture to the requisite temperature. The carbon dioxide thus obtained can be collected and utilised for any industrial purposes, for example for the manufacture of dry ice.

The mixture of calcium and magnesium oxides thus obtained is then' subjected to treatment in the manner previously described for the conversion of the magnesia into sulphide, whereafter, by reduction of the latter with calcium carbide magne ium is obtained.

EXAMPLE 3 Production of magnesium from magnesium sulphate The magnesium sulphate is first decomposed by heating it in the presence of carbon (such as coke) to a temperature of about 900 C., whereby carbon dioxide, sulphur dioxide, sulphur and magnesia are obtained. The magnesia so produced is treated with magnesium chloride, MgClz-GI-IzO. If so desired the magnesium chloride can be replaced by hydrochloric acid gas, the requisite proportion of this latter being employed to form the oxy-chloride, MgO-MgClz. The magnesium oxychloride in whichever way obtained is well dried and thereafter treated in the manner previously described so as to convert the oxide into the sulphide, a product of the composition MgS-MgClz being obtained. This product is then treated with calcium carbide whereby metallic magnesium is obtained.

It will of course be understood that any other magnesium ores or salts can be treated according to the general method herein described for the production of magnesium.

It will also be understood that the invention is not limited to the reduction of magnesium sulphide only, but that derivatives of magnesium sulphide, such as magnesium oxysulphide magne sium chloro-sulphide and mixtures thereof produced according to the present process, can be treated in the same manner with a carbide of an alkali earth metal, preferably with calcium carbide, for the production of magnesium.

Further, it may be mentioned that, products such as sulphur or carbon bisulphide employed in the present process are recovered for reuse in the process.

' the magnesium compound into magnesium sulphide; and thereupon reducing such magnesium sulphide, before its decomposition occurs, by the step of heating it in mixture with a reacting agent containing a carbide of another earth-alkali metal, in a non-oxidizing atmosphere free from moisture, air and nitrogen, and to a reacting temperature higher than that in the first reaction, namely, between about 1200 and 1600 (2., whereby magnesium vapours are formed and distilled off for separate condensation.

2. A continuous process for the industrial production of magnesium from magnesium compounds which consists in a first stage in producing magnesium sulphide by the heating of such magnesium compound with a reacting agent containing carbon and sulphur, in a non-oxidizing atmosphere free from moisture and air, and to a reacting temperaturewell inside the range between 800 and 1200 0., whereby to convert the bull: of the magnesium compounds into magnesium sulphide; and in the succeeding stage reducing such magnesium sulphide, before its decomposition occurs, by the step of heating it in finely divided mixture with a reacting agent containing a carbide of another earth-alkali metal, in a non-oxidizing atmosphere free from moisture, air and nitrogen, and to a reacting temperature higher than that in the first reaction, namely, inside the range between 1200 and 1600 0., whereby magnesium vapours are formed and distilled oif for separate condensation; while methodically removing byproducts including slag and replenishing the compounds and agents of said reactions.

3. The process as in claim 2 and wherein the second mentioned stage is performed with the assistance 01 a halide flux and at a temperature not greatly above 1200' C.

4. The process or claim 1 and wherein the first named reaction agent is a carbonaceous reducing agent in sulphur vapours.

5. The process or claim 1 and wherein the first named reaction agent is a gaseous vaporized nonmetallic sulphur compound.

6. The process oi claim 1 and wherein the first named reaction agent is carbon bisulphide vapor.

7. A continuous process for the industrial production of magnesium from magnesium oxychloride which consists in first heating dry magnesium oxychloride with a reacting agent con- 1200 and 1600 0., whereby magnesium vapoursare formed and distilled on: for separate condensation.

8. A continuous process for the industrial production of magnesium from calcined magnesite which consists in first producing magnesium suiphide by the step of heating such magnesite with a reacting agent containing carbon and sulphur, in a non-oxidizing atmosphere free from moisture and air, and to a reacting temperature of about 950 0., or more, whereby to convert the bulk or the magnesite into magnesium sulphi and thereupon reducing such magnesium s. bide, before its decomposition occurs, by the step of heating it in powdered mixture with a reacting agent containing a carbide or another earthalkali metal, in a non-oxidizing atmosphere tree from moisture, air and nitrogen, and to a reacting temperature higher than that in the first reaction, whereby magnesium vapours are formed and distilled oil for separate condensation.

9. A process as in claim 1 in which the reduction of the magnesium sulphide in the second step is eirected by heating it with calcium carbide in an atmosphere of a non-oxidizing gas.

10. A process as in claim 1, in which the magnesium obtained from the reduction of the magnesium sulphide is distilled ofl, conducted away and condensed into a molten metal with which it is to be alloyed.

DANIEL GARDNER. 

